This invention primarily relates to a multilayer substrate including resistors, capacitors, and wiring conductors therefor. A substrate of this type is herein called a monolithic multicomponents ceramic (MMC) substrate and is useful in, among others, manufacturing a piezoelectric oscillator, which may be a crystal oscillator.
Multilayer ceramic substrate including resistors, are already known. Such a substrate is manufactured by laminating a plurality of insulative green sheets and then firing or sintering the green sheets into an integral body of ceramic layers. Resistive and conductive patterns are preliminarily printed or otherwise formed on predetermined ones of the green sheets. When fired, the patterns become resistive and conductive films between the ceramic layers. The resistive and the conductive films serve as resistors and conductors for electrical connection thereto. Connection between the resistors or conductors on different ceramic layers is provided by conductive masses filled in via holes preliminarily formed through preselected ones of the green sheets. The conductors of the patterns and the conductive masses are herein referred to either singly or collectively as wiring conductors, which form an electrical circuit together with the resistors. The substrate may be used with a semiconductor chip, such as a silicon semiconductor chip, mounted thereon in electrical connection to the electrical circuit formed therein.
The green sheets have usually been manufactured of alumina. The alumina green sheets must be sintered at a high temperature, such as 1500.degree. C. or above. Even when the sintering is carried out in a reducing atmosphere, the high sintering temperature prohibits use of metals capable of providing fine conductive patterns. It is difficult to form via holes of a small diameter through the alumina green sheets. This makes it impossible to form dense wiring conductors and to render the substrate compact. Furthermore, the ceramic layers have a relatively large dielectric constant of about 10 and an appreciably large thermal expansion coefficient of about 70.times.10.sup.-7 /.degree.C. between room temperature and 250.degree. C. The large dielectric constant results in a long propagation delay. The large thermal expansion coefficient is incompatible with that of the silicon semiconductor chips.
On the other hand, piezoelectric oscillators are more and more widely used as clock generators and timing signal generators in recent communication apparatus as, for example, digital terminal equipment. A conventional piezoelectric oscillator may comprise a ceramic or like substrate and a piezoelectric oscillation element or vibrator, an active semiconductor device, at least one resistor, and at least one capacitor soldered or otherwise connected onto a printed circuit preliminarily formed on the substrate. The piezoelectric oscillation element, active semiconductor device, resistor or resistors, and capacitor or capacitors form an oscillation circuit in cooperation with the printed circuit. The oscillator is therefore bulky. The piezoelectric oscillation element as well as the active and passive circuit elements must be installed on the substrate one by one. Moreover, it is necessary for optimum operation of the oscillator to adjust the passive circuit elements by removing each undesirable element from the printed circuit and afresh installing a new one thereon. Manufacture of conventional piezoelectric oscillators of this type has therefore been time consuming and expensive.